Secretion of enkephalin-like peptides from adrenal glands into the circulation was studied in dogs with indwelling cannulae in the lumbar adrenal vein. Splanchnic nerve stimulation causes a voltage-dependent increase of met-enkeph-alin immunoreactive peptides and catecholamines in adrenal venous plasma. The effect of splanchnic nerve stimulation was mimicked by dimethylphenylpiperazinium and was blocked by hesamethonium. These results indicate that, similar to catecholamines, the release of met-enkephalin-like peptides from adrenal chromaffin cells is mediated through nicotinic receptors. Treatment of dogs with reserpine, unlike for catecholamines, did not impair storage of met-enkephalin-like peptides in adrenal chromaffin cells. Splanchnic nerve stimulation released the peptides into the adrenal vein at a similar rate as in saline-treated dogs. In reserpinetreated dogs splanchnic nerve stimulation caused a drop in arterial blood pressure, which was reversed by naloxone.